Collisional mafic magmatism of the fold-thrust belts framing southern Siberia (Western Sangilen,southeastern Tuva)     

R.A. Shelepaev  V.V. Egorova  A.E. Izokh  R. Seltmann 《Russian Geology and Geophysics》2018,59(5):525-540

We consider geochemical features of mafic magmatism manifested during the evolution of a complex nappe-folded structure in Western Sangilen, resulted from the Cambrian-Ordovician collisional tectogenesis. There are abundant ultramafic-mafic and mafic associations of different types in this region: layered low-Ti low-alkali ultramafic-mafic intrusions, high-Ti medium-alkali gabbroids, gabbro-monzodiorite intrusions, and alkali basalts. Isotope-geochronological data showed that these complexes formed over a wide time interval, from 570 to 440 Ma. At this time, the geodynamic setting in Western Sangilen changed from an island-arc one via a collision one to an intercontinental rift setting. At the early and late stages of the evolution of Western Sangilen, the geochemical features of mafites were typical of their geodynamic settings. The properties of mafites that formed synchronously with the collision are of particular interest. The studies have shown that the chemical composition of collisional mafites of Western Sangilen changed with time. They became richer in alkalies, titanium, and incompatible elements. This fact indicates a change in the type of mantle source from suprasubductional in the Cambrian to enriched deeper-level one in the Ordovician.  相似文献   

云南东川奚家坪玄武岩的地球化学特征、成因及其地质意义     

杨斌  周邦国  郭阳  王子正  廖震文  王生伟 《矿物岩石》2012,32(2):74-80

为了探讨云南东川地区奚家坪玄武岩的地球化学特征及其意义,本文以奚家坪玄武岩的地球化学分析数据为基础,在分析了其主微量和稀土元素的特征之后发现奚家坪玄武岩w(SiO2)为46.44%～49.56%,(K2O+Na2O)为2.6%～5.8%,在化学成分上属于钙碱性-低钾拉斑型过渡的岩石;其稀土元素的总量为80.98×10-6～102.77×10-6,LREE/HREE=0.78～1.11,表明在其形成过程中并没有发生过大规模的岩浆分异作用,因此化学成分基本可以反映出岩浆源区的化学组成特征。基于此,对奚家坪玄武岩其进行了源区性质、构造环境和可能的成因机制探讨,认为奚家坪玄武岩形成于拉张环境之中,很有可能是在昆阳裂谷形成初期形成,其岩浆来源于较富集的地幔源区,形成过程中几乎没有地壳物质参与。  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987113001138     

M.R.G. Sayyed 《地学前缘(英文版)》2014,5(6):791-799

Since continental sediments （in addition to the marine geological record） offer important means of deciphering environmental changes, the sediments hosted by the successive flows of the continental flood basalt provinces of the world should be treasure houses in gathering the palaeoclimatic data. Palaeosols developed on top of basalt flows are potentially ideal for palaeoenvironmental reconstructions because it is easy to determine their protolith geochemistry and also they define a definite time interval. The present paper summarizes the nature of the basalt-hosted palaeosols formed on the flood basalts provinces from different parts of the ~lobe havin~ different ages.  相似文献   

New recognition of Gaxue Formation and Zedang Formation in Yalu Tsangpo Suture Zone     

ZHANG Xinquan  WANG Jingui  ZHANG Zhenli  ZHUAN Shaopeng  ZHANG Liguo  CHENG Zhou  DENG Ke  HE Jiaoyue 《中国地质调查》2014,7(2):72-80

On the basis of the 1:50 000 regional geological survey, the authors comprehensively studied Gaxue Formation and Zedang Formation in North Yalu Tsangpo Suture Zone, and compared their petrogeochemical parameters and tectonic environment with ophiolite. Combined with paleontological and high-precision isotope dating analysis, it is preliminarily considered that Gaxue Formation, Zedang Formation and ophiolite are products of different genetic types. Gaxue Formation and Zedang Formation were formed in the intra-oceanic arc tectonic environment from late Jurassic to early Cretaceous, and belonged to the front arc basalt (FAB type) which was the standard oceanic plate stratigraphic sequence. In the late subduction and collision process, the main body of Gaxue Formation and Zedang Formation was transformed into melange or existed in the melange belt in the form of a broken clip (block), mainly as the structure styles in subduction and accretionary complex zones. This understanding is of great geological tectonic significance for the rational restoration and establishment of the northern belt oceanic plate stratigraphic sequence of Yalu Tsangpo Suture Zone.  相似文献   

Neoproterozoic Mafic Dykes and Basalts in the Southern Margin of Tarim, Northwest China: Age, Geochemistry and Geodynamic Implications   总被引：4，自引：0，他引：4  

ZHANG Chuanlin  YANG Dongsheng  WANG Hongyan  DONG Yongguan  YE Haimin 《《地质学报》英文版》2010,84(3):549-562

<正>Neoproterozoic rifting-related mafic igneous rocks are widely distributed both in the northern and southern margins of the Tarim Block,NW China.Here we report the geochronology and systematic whole-rock geochemistry of the Neoproterozoic mafic dykes and basalts along the southern margin of Tarim.Our zircon U-Pb age,in combination with stratigraphic constraint on their emplacement ages,indicates that the mafic dykes were crystallized at ca.802 Ma,and the basalt, possibly coeval with the ca.740 Ma volcanic rocks in Quruqtagh in the northern margin of Tarim. Elemental and Nd isotope geochemistry of the mafic dykes and basalts suggest that their primitive magma was derived from asthenospheric mantle(OIB-like) and lithospheric mantle respectively,with variable assimilation of crustal materials.Integrating the data supplied in the present study and that reported previously in the northern margin of Tarim,we recognize two types of mantle sources of the Neoproterozoic mafic igneous rocks in Tarim,namely the matasomatized subcontinental lithospheric mantle(SCLM) in the northern margin and the long-term enriched lithospheric mantle and asthenospheric mantle in the southern margin.A comprehensive synthesis of the Neoproterozoic igneous rocks throughout the Tarim Block led to the recognition of two major episodes of Neoproterozoic igneous activities at ca.820-800 Ma and ca.780-740 Ma,respectively.These two episodes of igneous activities were concurrent with those in many other Rodinian continents and were most likely related to mantle plume activities during the break-up of the Rodinia.  相似文献   

冀西北地区中侏罗世玄武岩的首次发现及其地质意义     

白春东  许凡  李泽阳  孟家葆  朱本鸿 《地质论评》2024,70(3):1127-1138

笔者等在张家口市宣化区—涿鹿县一带中—上侏罗统髫髻山组底部首次发现玄武岩组合,其时代归属、地球化学性质及地质意义需要开展研究。本文对玄武岩开展地质学、岩石学、地球化学和同位素年代学研究。玄武岩SiO2含量为39. 49%～49. 74%,Mg#为28～65,里特曼指数σ主要为2. 61～33. 12。玄武岩获得LA- ICP- MS锆石U- Pb年龄为164. 3±2. 6 Ma,时代为中侏罗世,代表髫髻山组底界年龄。玄武岩属于碱性玄武岩系列,与上覆粗面岩构成双峰式火山岩组合,表明髫髻山组早期火山岩形成于大陆板内拉张环境。该套玄武岩是髫髻山组中性火山岩的玄武质岩浆底侵作用的地质学、岩石学和大地构造学证据。  相似文献   

滇西丽江树底桥及宁蒗万马场二叠纪玄武岩地球化学特征及成因     

倪平泽  肖龙  何琦  魏启荣 《矿物岩石》2007,27(1):107-116

滇西丽江及宁蒗、永胜地区广泛分布二叠纪玄武岩,它们可能是峨眉山大火成岩省的一部分。通过对丽江树底桥及宁蒗万马场二叠纪玄武岩进行的地球化学系统采样研究,认为这些玄武岩富集大离子亲石元素及高场强元素,具有与洋岛玄武岩相似的地球化学特征。与典型的峨眉山玄武岩地球化学成分的对比研究认为其属于峨眉山高钛玄武岩,为峨眉山地幔柱活动的产物。利用稀土元素进行反演模拟,估算高钛玄武岩源区的成分及岩浆的演化趋势,模拟计算结果显示,丽江树底桥玄武岩可能来自于尖晶石二辉橄榄岩与石榴石二辉橄榄岩的过渡源区(尖晶石∶石榴石=65∶35～1∶1)2%～3%的部分熔融,并经历了以单斜辉石为主的分离结晶作用(5%～15%);万马场玄武岩来自于相似的源区(尖晶石∶石榴石=45∶55～1∶1)3%左右的部分熔融,分离结晶程度≤5%。  相似文献   

华北地区中生代玄武岩高Nb/Ta值对地壳岩石再循环的直接记录   总被引：5，自引：0，他引：5  

刘勇胜  高山 《矿物岩石地球化学通报》2007,26(1):19-28

为揭示中国东部中生代大规模岩石圈减薄作用的深部地幔地球化学响应,对华北东部5个地区的中生代玄武岩进行了ICP-MS分析。结果表明,119~125 Ma玄武岩不仅具显著分异的稀土元素组成(La/Yb=35~60)、岛弧玄武岩型微量元素分布特征,且具高Ni(210×10-6~510×10-6)和Cr(510×10-6~1400×10-6)含量、高Mg#(71~78),以及系统高于球粒陨石的Nb/Ta值[19.9±1.0(1σ),n=16];而100 Ma碱锅玄武岩具有与球粒陨石(17.6)接近的Nb/Ta值[17.3±0.2(1σ)]。再循环地壳岩石在金红石稳定域内以榴辉岩为残余的部分熔融体 地幔橄榄岩反应,不仅使地幔岩石熔点降低、获得高Nb/Ta值及石榴子石特征,而且橄榄石向辉石的转变反应使Ni和Cr在交代地幔中的总分配系数显著降低。受熔体交代地幔橄榄岩的部分熔融可合理解释119~125 Ma玄武岩的上述地球化学特征,玄武岩Nb/Ta值应是对岩石圈减薄过程中地壳物质返回地幔后熔融产生硅质熔(流)体对上覆地幔交代的直接地球化学记录。  相似文献   

大火成岩省及地幔动力学   总被引：4，自引：1，他引：4       下载免费PDF全文

赵海玲  狄永军  李凯明  李永华 《岩石矿物学杂志》2001,20(3):307-312

大火成岩省由一个体积巨大的、连续的、以富镁铁岩石占优势的喷出岩及其伴生的侵入岩组成，是一个全球现象。它包括大陆溢流玄武岩和伴生的侵入岩，火山被动边缘玄武岩，大洋高原、海岭、海山群和洋盆溢流玄武岩。Ontong Java和Kerguelen-Broken Ridge大洋高原、北大西洋火山被动边缘、德干和哥伦比亚河大陆溢流玄武岩是3个主要大火成岩省的典型代表。各种不同的大火成岩省在时空分布及组成上都具有相似性，它们具有非常大的体积、高的喷发速率，岩石类型以拉斑玄武岩为主。大火成岩省代表了地球上已知的最大的火山岩浆活动，记录了物质和能量从地球内部向外的大量转换。大火成岩省难以用板块构造来解释，可用热柱模式来解释，通常被认为是与来自下地幔的热柱“头”有关。大火成岩省是地球动力学过程在地壳的表现，因此大火成岩省参数可作为边界条件去反演地幔动力学过程。  相似文献